There is a website that I like visiting which uses a Javascript that does not work on Linux with Iceweasel. Looking into the source, I have found a simple way to fix it, so what I would like to do is set up something like Fiddler2's AutoResponder feature that will intercept a request for the bad Javascript, returning the fixed Javascript from the local filesystem instead.

What is the simplest way to do this?

Note: The webmaster has refused to use my fixed version of the script.